Many types of building structures are supported by foundations that in turn are supported by soil rather than by more stable bedrock or other supporting strata. Shifting of the supporting soil over time can cause the foundation to sink, which can lead to various problems including structural damage. Unless the foundation is supported, further shifting can occur and worsen the structural damage. Furthermore, it is frequently desirable to raise the foundation to its original level in order to facilitate restoration of the structure to a proper condition.
Accordingly, many devices and methods have been developed or proposed for raising and supporting a foundation. Many such devices and methods employ piers that are driven into the ground adjacent an edge of the foundation until the piers encounter bedrock or other relatively firm supporting strata. Jacking devices are used for jacking up the edge of the foundation, using the piers for support. When the foundation is raised to the desired level, the foundation is affixed to the piers and the jacking equipment is removed.
In some such lifting devices, brackets are affixed to the foundation and are slidably engaged with the piers, and the jacking devices engage the brackets for raising the foundation. A bracket typically includes a pier-receiving portion such as a collar or sleeve that surrounds the pier in close-fitting fashion, and a support plate rigidly affixed to the pier-receiving portion and configured to engage a lower surface of a foundation. The pier-receiving portion is sized to fit closely about the pier so that the bracket is able to slide upward and downward along the pier but is substantially prevented from moving in any other direction. A disadvantage of this approach is that substantial bending moments can be exerted on the pier if the support plate is at an angle other than perpendicular to the pier, such as may occur if the foundation changes its orientation during a lifting operation. In some cases, bending moments great enough to cause failure of the pier can be exerted as a result of misalignment between the foundation and the pier. Furthermore, misalignment between the bracket and the foundation can result in point loads being exerted on the foundation, which in some cases can cause damage to the foundation, such as cracking.
U.S. Pat. No. 5,213,448 discloses an underpinning bracket for a foundation, in which a sleeve is placed over the upper end of an anchor rod screwed into the ground adjacent the edge of a foundation. The sleeve is bonded to the anchor rod. A bracket is slidably received over the sleeve and attached to the foundation. A jack is used for raising the bracket upward along the sleeve. The amount of vertical lift that can be achieved is limited by the length of the sleeve, since the bracket must be mounted about the sleeve. The '448 patent does not address the problem of misalignment between the bracket and the foundation.